Photoelectric conversion element and process for fabricating the same, electronic apparatus and process for fabricating the same, and semiconductor layer and process for forming the same

Abstract

A paste in which semiconductor fine grain such as titanium oxide fine grain or the like and a binder made of a polymer compound are mixed is coated onto a transparent conductive substrate and sintered, thereby forming a semiconductor layer made of the semiconductor fine grain, after that, ultraviolet rays are irradiated to the semiconductor layer and, by using a photocatalyst effect of the semiconductor fine grain, an organic substance remaining in the semiconductor layer is removed.

Description

TECHNICAL FIELD [0001] The invention relates to a photoelectric conversion device, its manufacturing method, an electronic apparatus, its manufacturing method, a semiconductor layer, and its manufacturing method and is suitable when it is applied to, for example, a photoelectric conversion device using a semiconductor layer made of semiconductor fine grain, particularly, a semiconductor layer made of semiconductor fine grain sensitized by dye. BACKGROUND ART [0002] Since a solar cell as a photoelectric conversion device to convert sunlight into an electric energy uses the sunlight as an energy source, an influence that is exercises to the global environment is extremely small and it is expected to be spread further. [0003] Various materials have been examined as a material of the solar cell and a number of solar cells using silicon have been commercialized. They are mainly classified into: a crystalline silicon solar cell using single crystal silicon or poly crystal silicon; and an ...

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Benefits of technology

[0022] Although the grain diameter of the semiconductor fine grain is not particularly limited, it is preferable to set the mean grain diameter of the primary particle to 1 to 200 nm, particularly preferably, 5 to 100 nm. It is also possible to mix semiconductor fine grain whose mean grain diameter is larger than such a mean grain diameter to the semiconductor fine grain of such a mean grain diameter, scatter incident light by the semiconductor fine grain of large mean grain diameters, and improve quantum efficiency. In this case, it is desirable that the mean grain diameter of the semiconductor fine grain to be additionally mixed is equal to 20 to 500 nm.

[0023] Generally, the more a thickness of semiconductor layer comprising the semiconductor fine grain increases, the more an amount of adsorbed dye per unit projection area increases, so that a capturing ratio of the light rises. However, since a diffusion length of the injected electrons increases, a loss caused by charge recombination also increases. Therefore, although a preferable thickness of semiconductor layer exists, it is generally equal to 0.1 to 100 μm, preferably, 1 to 50 μm, particularly preferably, 3 to 30 μm. To increase a surface area of the semiconductor fine grain, remove impurities of the semiconductor layer made of the semiconductor fine grain, and raise electron injecting efficiency upon injecting electrons from the dye into the semiconductor fine grain, for example, a chemical process using a titanium tetrachloride aqueous solution or an electrochemical process using a titanium trichloride aqueous solution can be also performed. A conductive assistant can be also added to reduce an impedance of the semiconductor layer made of the semiconductor fine grain.

[0032] A smaller sheet resistance of the transparent conductive substrate is better. Specifically speaking, the sheet resistance of the transparent conductive substrate is preferably set to 500 Ω / cm2 or less, more preferably, 10 Ω / cm2 or less. In the case of forming the transparent electrode onto the transparent supporting substrate, any type of material can be fundamentally used so long as it has the conductivity and transparency. However, it is desirable to use indium-tin composite oxide (ITO), fluorine doped SnO2 (FTO), SnO2, or the like from a viewpoint that they have the conductivity, transparency, and further, heat resistance at high levels. ITO is preferable among them in consideration of the costs. It is also possible to combine two or more kinds of those materials and use them. To reduce the sheet resistance of the transparent conductive substrate and improve the collecting efficiency, metal wirings having the high conductivity can be also patterned onto the transparent conductive substrate.

[0033] An arbitrary electrode can be used as a counter electrode so long as it is made of a conductive substance. An insulative substance can be also used so long as a conductive layer is formed on the side where it faces the semiconductor layer. However, it is desirable that a material which is electrochemically stable is used as an electrode material. Specifically speaking, it is preferable to use platinum, gold, conductive polymer, carbon, or the like. To improve the catalyst effect of the redox reaction, it is desirable that the electrode on the side where it faces the semiconductor layer has a fine structure and its surface is increased. For example, in the case of platinum, it is desirable to be in the platinum black state and in the case of carbon, it is desirable to be in the porous state. The platinum black state can be formed by an anode oxidizing method, a platinum chloride acid treatment, or the like of platinum. Carbon in the porous state can be formed by a method of sintering carbon fine grain, a method of sintering an organic polymer, or the like.

[0034] The electrolyte becomes a carrier transfer layer and is constructed by a redox species and a solvent. Specifically speaking, the redox species is constructed by, for example, a combination of iodine (I2) and an iodine compound (metal iodide, organic iodide, or the like) or a combination of bromine (Br2) and a bromine compound (metal bromide, organic bromide, or the like). Further, there can be used: metal complexes such as ferrocianic acid salt / ferricianic acid salt, ferrocene / ferricynium ions, or the like; sulfur compounds such as polysodium sulfide, alkylthiol / alkyl disulfide, or the like; viologen dye; hydroquinone / quinone; or the like. As cations of the above metal compound, it is suitable to use Li, Na, K, Mg, Ca, Cs, etc. As cations of the above organic compound, it is suitable to use a quaternary ammonium compound such as tetraalkyl ammoniums, pyridinums, imidazoliums, or the like. However, the cations are not limited to them and it is also possible to combine two or more kinds of those elements and use the mixture as necessary. Among them, an electrolyte obtained by combining I2 with quaternary ammonium compound such as LiI, NaI, imidazolium iodide, or the like is suitable. A concentration of electrolyte salt is preferably set to 0.05 to 5 M for the solvent and, further preferably, 0.2 to 1 M. A concentration of I2 or Br2 is preferably set to 0.0005 to 1 M and, further preferably, 0.0001 to 0.1 M. To improve a release voltage and a short-circuit current, various additives such as 4-tert-butyl pyridine, 2-n-propyl pyridine, carboxylic acid, and the like can be also added.

[0054] According to the invention constructed as mentioned above, the paste in which the semiconductor fine grain and the binder made of the polymer compound are mixed is coated and sintered, thereby forming the semiconductor layer made of the semiconductor fine grain. After that, by irradiating the ultraviolet rays to the semiconductor layer, the organic substance remaining in the semiconductor layer is oxidization dissolved by the photocatalyst effect of the semiconductor fine grain, becomes carbon dioxide, water, and the like, and is removed. Particularly, by sufficiently irradiating the ultraviolet rays, it is possible to realize the state where the organic substance does not substantially remain in the semiconductor layer. As disclosed in Non-Patent Document 2, if the semiconductor fine grain is made of titanium oxide, the surface changes to the surface having hydrophilicity (the surface hydroxyl group increases), so that a binding force between the semiconductor fine grain increases and the electron movement between the semiconductor fine grain becomes easy. At the same time, if the semiconductor fine grain is made of titanium oxide, a coupling force between the sensitizing dye and a carboxyl group is also increased due to an increase in surface hydroxyl group. The electron movement between the dye and the semiconductor fine grain made of titanium oxide also becomes easy. Consequently, the photoelectric conversion efficiency is improved.

Problems solved by technology

However, in the crystalline silicon solar cell, although photoelectric conversion efficiency indicative of performance of converting the light (solar) energy into the electric energy is higher than that of the amorphous silicon solar cell, since a large energy and a long time are required for a crystal growth, productivity is low and it is disadvantageous in terms of costs.

Further, in the amorphous silicon solar cell, although the productivity is higher than that of the crystalline silicon solar cell, a vacuum process is necessary upon manufacturing in a manner similar to the crystalline silicon solar cell and a facility related cost is still heavy.

However, since most of those solar cells have the low photoelectric conversion efficiency of about 1%, they are not put into practical use.

This obstructs combination of the semiconductor fine grain, resulting in deterioration of the photoelectric conversion efficiency.

Also in this case, the photoelectric conversion efficiency deteriorates.

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